1. Field of the Invention
The present invention relates to a patch antenna apparatus, and more particularly, a patch antenna apparatus mainly for use in an antenna apparatus for a base station of mobile communication systems.
2. Description of the Prior Art
FIG. 29 is a perspective view showing a configuration of a prior art patch antenna apparatus. FIGS. 30 to 32 are pattern diagrams each showing an example of the projection directional pattern of the patch antenna apparatus of FIG. 29.
Referring to FIG. 29, a dielectric substrate 90 has a top surface and a bottom surface which are parallel to each other, and a grounding conductor 91 is formed on the bottom surface of the dielectric substrate 90. On the top surface of the dielectric substrate 90 is formed a square-shaped conductor patch 92 having a square which has one side having a length of half a wavelength of a resonance frequency when the dielectric constant of the dielectric substrate 90 is taken into consideration. For example, the conductor patch 92 is formed so that, on an X-Y plane having the origin located in the center of the dielectric substrate 90, sides of the square of the conductor patch 92 which cross each other so as to be perpendicular to each other are parallel to the X-axis and Y-axis, respectively, and the center of the conductor patch 92 is positioned at the origin of the X-Y plane. Further, a feeding point 93 is positioned on the X-axis, namely, is located on the perpendicular bisector of one side in the Y-axis direction of the square of the conductor patch 92. When a radio signal having the above-mentioned resonance frequency is fed to the feeding point 93, the patch antenna apparatus resonates in parallel with the X-axis. Consequently, the radio signal is projected, as a linearly polarized radio wave having the exciting or driving direction parallel to the X-axis including the feeding point 93, in the Z-axis direction which is perpendicular to the X-Y plane and opposite to the grounding conductor 91.
As shown in FIGS. 30 to 32, the radio wave projected from the patch antenna apparatus of FIG. 29 has a main polarization which is a linear polarization having the exciting or driving direction parallel to the X-axis. The radio wave is projected so that its projection intensity becomes the maximum in the Z direction which is the front direction of the patch antenna apparatus.
However, the prior art patch antenna apparatus shown in FIG. 29 can project the linearly polarized radio wave which is parallel to the X-axis but cannot project a linear polarization parallel to the Y-axis which is perpendicular to the X-axis. Although the patch antenna apparatus can strongly project the radio wave in the Z direction which is the front direction of the antenna apparatus, the patch antenna apparatus cannot strongly project the radio wave in the horizontal direction of the antenna apparatus and an upper direction inclined with a low elevation angle.
For example, in the case of projecting the radio wave in a space such as a room or the like whose height is small and which has a broadening in the horizontal direction, it can be considered that the antenna apparatus is provided on a ceiling or a wall surface. In consideration of the view or the like, however, it is desirable to install the antenna apparatus on the ceiling which is not usually seen. In the case of suspending the antenna apparatus from the ceiling, in order to efficiently project the radio wave, it is preferable to horizontally suspend the antenna apparatus from the ceiling so that the plane of the dielectric substrate 90 is parallel to the surface of the ceiling (hereinafter, this installing method will be referred to as a ceiling installing method). In this case, the radio wave projected from the patch antenna apparatus has only a polarization which is parallel with the X-axis. Mainly, a vertical polarized radio wave is used in mobile communication systems. In the ceiling installing method, however, the intensity of the vertical polarized radio wave in radio waves projected from the antenna apparatus is the strongest on the X-axis and no vertical polarized radio wave exists in radio waves projected from the antenna apparatus on the Y-axis.
In the case of a space such as a room or the like whose height is small and which has a broadening in the horizontal direction, in order to realize a broader projection area, it is desirable that the radio wave is strongly projected from the antenna apparatus in the horizontal direction of the antenna apparatus and an upper direction inclined with a low elevation angle.